Apparatus and oil compositions containing olefin dimer products

ABSTRACT

Heat transfer, lubricating, functional and/or insulating fluid compositions for use in apparatus such as electrical transformers contain up to 25 weight percent of one or more oil additives and a 1-octene and/or 1-decene dimer and/or a 1-octene and 1-decene co-dimer oil having improved low temperature properties which oil contains less than about 2.5 weight percent of, respectively, the 7-methylpentadecene, 9-methylnonadecene and, 7- and 9-methylheptadecene isomers. The dimers can be hydrogenated to provide the saturated counterparts of the isomers.

This application is a division of application Ser. No. 705,960, filedMay 28, 1992, Pat. No. 5,171,918, which is a continuation-in-part of aapplication Ser. No. 684,291, filed Apr. 12, 1991, abandoned, which is acontinuation-in-part of application Ser. No. 554,717, filed Jul. 19,1990, Pat. No. 5,068,487, both of which applications Ser. No. 684,291now abandoned, and Ser. No. 554,727 now U.S. Pat. No. 5,068,487, areincorporated herein by reference.

BACKGROUND

This invention relates generally to alpha-olefin oligomers which areuseful as synthetic lubricants and functional fluids and moreparticularly to apparatus and fluids which contain alpha-olefin dimerproducts having improved low temperature properties which can beprepared by a BF₃ -promoter catalyst system using alcohol alkoxylates aspromoters.

Alpha-olefin oligomers and their use as synthetic lubricants("synlubes") are well-known. The oligomers are usually hydrogenated inorder to improve their stability. Early reports of such synlubes are inSeger et al. U.S. Pat. No. 2,500,161 and Garwood U.S. Pat. No.2,500,163. The particular applications for which such oligomer oils areused depends upon their viscosity, with viscosities of about 2-10 cSt at100° C. being preferred for general lubricating oil applications. Lowviscosity, (e.g. 1-3 cSt at 100° C.) alpha-olefin dimer oils areespecially useful in heat transfer, insulating, hydraulic and lowtemperature lubricant applications.

Co-pending application Ser. No. 554,727 describes a process forpreferentially making dimer oils of linear alpha-olefins such as1-octene and 1-decene by using a catalyst comprising boron trifluorideand an alcohol alkoxylate promoter such as 2-methoxyethanol. Thisprocess produces dimer products which have improved low temperatureproperties compared to dimers prepared using other alcohol promoterssuch as propanol or butanol. These dimer products of 1-decene or1-octene remain clear, without precipitation of components at -54° C.The products have a unique isomer content in that they containundetectable amounts (less than about 0.5% by weight) of, respectively,the nearly straight chain isomers 9-methylnonadecenes and7-methylpentadecenes or, after hydrogenation of the dimer products, thesaturated counterparts of these compounds. In contrast, commerciallyavailable hydrogenated dimers prepared, for example, by oligomerizing1-decene using a BF₃ -butanol, or BF₃ -propanol catalyst have asignificantly different isomer content than those produced using thealcohol alkoxylate promoters and contain much greater amounts (3 to 5weight percent) of relatively linear isomers, e.g. 9-methylnonadecane,and become cloudy and exhibit significant viscosity changes at -54° C.

BRIEF SUMMARY

In accordance with this invention there is provided an apparatuscontaining a heat transfer, lubricating, functional and/or insulatingfluid which comprises a dimer of 1-octene which is a mixture of C₁₆ H₃₂isomers containing less than about 2.5 weight percent of7-methylpentadecene isomers and/or a dimer of 1-decene which is amixture of C₂₀ H₄₀ isomers containing less than about 2.5 weight percentof 9-methylnonadecene isomers and/or a co-dimer of 1-octene and 1-decenewhich is a mixture of C₁₈ H₃₆ isomers containing less than about 2.5weight percent of the 7-methylheptadecene and/or 9-methylheptadeceneisomers.

Also provided is a heat transfer, lubricating, functional and/orinsulating fluid composition which comprises (i) a 1-octene and/or a1-decene dimer and/or a 1-octene and 1-decene co-dimer oil comprising amixture of isomers which in the case of the 1-octene dimer are C₁₆ H₃₂isomers containing less than about 2.5 weight percent of the7-methylpentadecene isomers, in the case of the 1-decene dimer are C₂₀H₄₀ isomers containing less than about 2.5 weight percent of the9-methylnonadecene isomers, and in case of the co-dimer are C₁₈ H₃₆isomers containing less than about 2.5 weight percent of the7-methylheptadecene and/or 9-methylheptadecene isomers, and (ii) fromabout 0.1 to 25 weight percent of fluid composition of one or more oiladditives. The dimers can be hydrogenated to provide the saturatedcounterparts of the isomers, i.e. C₁₆ H₃₄ for the I-octene dimer, C₁₈H₃₈ for the co-dimer and C₂₀ H₄₂ for the 1-decene dimer.

DETAILED DESCRIPTION

The dimer products useful in this invention are preparable by theprocess described in co-pending application Ser. No. 554,727. Accordingto the process, the 1-octene or 1-decene linear alpha-olefin monomer ora mixture of such monomers in any proportions is contacted with acatalytic amount of boron trifluoride which should be at least about0.002 moles per mole of olefin. When a mixture of 1-octene and 1-deceneis dimerized some 1-octene and 1-decene dimers are produced besides theco-dimer. Such mixtures can be employed in the invention withoutseparating out the co-dimer. Preferably the reaction mixture issaturated with BF₃. The boron trifluoride is used in combination with apromoter which is an alcohol alkoxylate. This promoter surprisinglyfavors the production of lower oligomers and particularly productscontaining predominantly dimer and trimer with a dimer to trimer ratioof greater than about one. Under ordinary reaction conditions the dimerdoes not further react, and particularly does not dimerize, to anysignificant extent so that the reaction is easily controllable toproduce a large proportion (at least about 40 and preferably 50 to 85weight percent or more dimer based on the total weight of oligomers inthe product) of dimer. The dimer content asymptotically approaches amaximum rather than sharply peaking at a transient maximum, which iscommon in prior processes. The dimer products are a complex mixture of25 or more isomers (a C₂₀ H₄₂ paraffin can theoretically have 366,319possible isomers). There is no absolute method for predicting theisomers most likely to be found in the hydrogenated dimer products of1-decene products. Accordingly, analysis of all of the isomers by gaschromatography is not practical, especially since peaks can be mixturesof closely related isomers (see Onopchenko, et al., "BF₃ -CatalyzedOligomerization of Alkenes: Structures, Mechanisms, and Properties",Ind. Eng. Chem. prod. Res. Dev. 1983, 22, 182-191). However, it ispossible to identify the more linear isomers such as those having nobranches or a single branch with one carbon atom. The dimer productsprepared using the alcohol alkoxylate promoters have improved lowtemperature properties because of their unique isomer content in thatthey contain less than about 2.5 weight percent and, especially, lessthan about 0.5 weight percent of relatively linear isomers.

Alcohol alkoxylates useful in the invention can be represented, forexample, by the formula:

    RO(CHR'--CHR"--(CHR'").sub.m --O).sub.n H

where m is 0, 1 or 2, R is hydrocarbyl containing from 1 to 24 carbons,including mixtures thereof, R', R" and R'" are independently hydrogen,methyl, or ethyl and when m is 2, each R'" can be different, and naverages 1 to 15.

Examples of such alcohol alkoxylates include glycol ethers such asethylene glycol monomethyl ether (2-methoxyethanol) and propylene glycolmonoethyl ether and the like and ethoxylates derived from mixed C₂ toC₂₄, preferably C₂ to C₁₈ and most preferably C₆ to C₁₂ straight chainalcohols. Suitable ethoxylates where R' and R" are hydrogen and m in theformula is 0, and n in the formula averages about 2 to 12, andpreferably 3 to 6, are commercially available under the Ethonictrademark.

The promoters are used in minor, effective amounts, for example, fromabout 0.001 to 0.040 moles per mole of alpha-olefin monomer (0.1 to 4.0mole percent). In general, the BF₃ is used in molar excess to the amountof promoter. This can be accomplished by using a closed reactor and asmall BF₃ pressure over the reaction mixture. The promoter can be mixedwith the olefin feed and the reaction can be carried out in a batch orcontinuous process at temperatures of about 0° C. to 200° C. andpressures ranging from atmospheric up to, for example, 1,000 psig. Thereaction temperature will change the oligomer distribution withtemperatures of about 50° C. and above favoring the production of loweroligomers, namely dimer. Preferred reaction temperatures and pressuresare about 20° C. to 65° C. and 5 to 100 psig.

The oligomer mixture from the reaction contains monomer which can beremoved by distillation. The monomer has been found to contain mostlyless reactive, isomerized material. However, this monomer can berecycled because it will react to form oligomers in the presence offresh alpha-olefin monomer. For example, portions of up to about 25weight percent and preferably 5 to 15 weight percent recycled monomerbased on total monomer can be mixed with fresh monomer. The productmixture can be further separated by distillation to provide one or moreproduct fractions having the desired viscosities for use in variouslubricant applications such as drilling, hydraulic or metal workingfluids, gear oils and crankcase lubricants.

The alcohol alkoxylates in the presence of BF₃, form stable complexeswhich separate from the product mixture on standing and can be readilyrecovered and reused. This avoids the BF₃ separation and recoveryprocedures necessary when using, for example, a BF₃ -butanol complex. Infact, because the alcohol ethoxylates are surfactants, it is preferableto let the catalyst settle from the reaction mixture prior to quenchingwith base, and especially when using NaOH, in order to avoid theformation of an emulsion.

The oligomer product can be hydrogenated by conventional methods.Supported nickel catalysts are useful. For example, nickel on aKieselguhr support gives good results. Batch or continuous processes canbe used. For example, the catalyst can be added to the liquid andstirred under hydrogen pressure or the liquid may be trickled through afixed bed of the supported catalyst under hydrogen pressure. Hydrogenpressures of about 100 to 1,000 psig at temperatures of about 150° to300° C. are especially useful.

The preparation of the fluids for use in the invention is furtherillustrated by, but is not intended to be limited to, the followingexamples in which the oligomerizations are performed in a three pintstirred reactor consisting of a glass reactor bowl, glass jacket, and astainless steel top. The reactor is equipped with an air driven magneticdrive stirrer with a marine propeller, a heating/cooling coil andcirculating system, dip tube, gas inlet and outlet valves and a pressurerelief valve.

Examples 1-5

1-Decene (600.0 grams, 4.29 moles) and 1.0 mole % based on 1-Decene ofEthonic® 610-3, (which is a C₆ to C₁₀ mixed alcohol ethoxylate having anaverage of three --CH₂ --CH₂ O) groups), are charged into the reactorwhich is then assembled and purged with N₂ with gentle agitation for 30minutes. During this time the reactor is brought up to the appropriatereaction temperature by the heating coil circulating system. The reactoris then pressurized (N₂) to 20 psig to insure that no leaks exist. Afterthe pressure is relieved the stirring rate is increased and BF₃ isintroduced into the reactor via a sparge tube located below the surfaceof the liquid. After a brief (5-10 seconds) purge, the system ispressurized to 10 psig with BF₃. The reaction is stopped after thechosen reaction time by venting the BF₃ through a 10 weight percent NaOHscrubber and quenching with either 5% aqueous NaOH (Examples 2 and 3) orsaturated Na₂ SO₄ (Examples 1, 4 and 5) (50-150 ml). The reactor ispurges with dry N₂ until all of the BF₃ is removed. The polyalphaolefin(PAO) - unreacted decene mixture is washed several times with water,dried over anhydrous CaCl₂, and filtered. The product content isdetermined by gas chromatographic analysis. The reaction times,temperatures and product analysis are given in Table 1 .

                  TABLE 1                                                         ______________________________________                                                                 GC Area                                              Ex-   Time    Temp.      %.sup.1 Di-  Tri- Tetra-                             ample (min)   (°C.) [Max.]                                                                      Monomer mer  mer  mer                                ______________________________________                                        1     120     20 [28]    11      41   42   6                                  2     120     32 [39]    15      48   32   4                                  3     120     45 [50]    23      48   20   9                                  4      60     45 [52]    29      50   19   3                                  5     120     80 [86]    14      68   16   3                                  ______________________________________                                         .sup.1 Where area % ˜ weight %                                     

Example 6

The process of Example 2 is repeated except at double the amount ofalcohol ethoxylate (4 wt %/2 mole %) and quenching is with saturated Na₂SO₄. The product distribution in gas chromatography area percent is 9%monomer, 48% dimer, 37% trimer and 6% tetramer.

Example 7

The process of Example 3 is repeated except that quenching is withsaturated Na₂ SO₄ and 9.1 weight percent of the decene monomer isrecycled, considerably isomerized monomer from a previous reaction. Theproduct distribution in gas chromatography area percent is 20% monomer,52% dimer, 24% trimer and 5% tetramer.

Example 8

The process of Example 2 is repeated except that Ethonic® 810-6 (2.8 wt%, 1.0 mole %) which is a C₈ to C₁₀ mixed alcohol ethoxylate having anaverage of six --CH₂ --CH₂ O) groups is used as the promoter andquenching is with saturated Na₂ SO₄. The product distribution in gaschromatography area percent is 24% monomer, 46% dimer, 26trimer and 4%tetramer.

The dimer fractions from Examples 1, 2 and 3 are separated bydistillation and hydrogenated. Their physical properties are reported inTable 2 where the composition is given in gas chromatography areapercent.

                  TABLE 2                                                         ______________________________________                                        Example     1          2          3                                           ______________________________________                                        Monomer     --         0.5        0.7                                         Dimer       98.9       96.7       97.9                                        Trimer      1.1        2.6        1.4                                         Tetramer    --         0.2        --                                          KV.sub.100° C. (cSt)                                                               1.71       1.66       1.63                                        KV.sub.40° C. (cSt)                                                                5.22       4.99       --                                          KV.sub.-40° C. (cSt)                                                               266.0      251.0      257.0                                       Pour point (°C.)                                                                   <-65       <-65       <-65                                        Flash Point (°C.)                                                                  160.0      148.0      152.0                                       ______________________________________                                    

This example illustrates the recycle of the promoter/-BF₃ co-catalystcomplex.

1=Decene (600.0 g, 4.29 mol) and Ethonic® 610-3 ethoxylate (11.79 g,42.9 mmol) are charged into the reactor which is then assembled andpurged with N₂ with gentle agitation for 30 minutes; during this timethe vessel temperature is brought up to 45° C. The reactor is thenpressurized (N₂) to 20 psig to insure that no leaks exist. After thepressure is relieved, the stirring rate is increased and BF₃ isintroduced into the reactor via a sparge tube located below the surfaceof the liquid. After a brief (5-10 seconds) purge, the system ispressurized to 10 psig with BF₃. Periodic samples are collected andquenched with saturated aqueous Na₂ SC₄, washed with water (twice),dried over anhydrous CaCl₂, filtered through syringe disk filters, andanalyzed by gas chromatography.

After 60 minutes, the BF₃ is purged from the reactor with N₂ for about30 minutes. The stirring is then stopped to allow the two existingphases to separate (˜20 minutes). The upper layer (product 9A) is thendrained and washed with 5% aqueous NaOH followed by 2 water washes. Thelower layer (co-catalyst) remains in the reactor.

At this point more 1-decene is added and a second reaction initiated bypressurizing the reactor with BF₃ (no additional Ethonic® 610-3 isadded). After 60 minutes the mixture is again purged with N₂, allowed tosettle (20 minutes), and the PAO drained (9B). This procedure isrepeated once more to collect a third lot of PAO (9C).

After the third run, the co-catalyst layer is kept in the reactor underan atmosphere of BF₃ /N₂. After 20 hours another run (120 minutes) ismade to collect a fourth lot of PAO (9D). Again, after an additional 20hours, a fifth run is made (9E). Results are tabulated in Table 3.

                  TABLE 3                                                         ______________________________________                                                Time    GC Area %                                                     Reaction                                                                              (min)   Monomer     Dimer Trimer                                                                              Tetramer                              ______________________________________                                        9A      60      26          50    21    3                                     9B      60      44          42    12    1                                     9C      60      46          41    12    1                                     9D      120     29          54    16    2                                     9E      120     34          50    14    1                                     ______________________________________                                    

The results illustrate that the co-catalyst can be easily recycled andremains effective in providing high yields of dimer.

Example 10

Example 3 is repeated using 2-methoxyethanol promoter at a concentrationof 1 mole percent based on monomer. After two hours the gaschromatography area percent product distribution is 8% monomer, 77%dimer, 13% trimer and 2% tetramer or about 85% dimer based on totaloligomer product with a conversion to oligomer of over 90. Repeating theprocess at double the promoter concentration [2.0 mol % (1.0 wt %)] gaveabout the same result in half the time (one hour instead of two). Thisexample illustrates that an oligomer which is close to a 2 cSt (at 100°C.) viscosity product can be produced by merely removing the monomer.

Comparison

A product prepared from 1-decene monomer using a BF₃.n-butanol catalyst(1.3 mole percent n-butanol on monomer) at a reaction temperature of 40°C. and 20 psig BF₃ pressure typically gives a gas chromatography areapercent product distribution of about 1% monomer, 2% dimer, 52% trimer,28% tetramer, 11% pentamer, and 5% hexamer.

Samples of eicosane (linear C₂₀) and 9-methylnonadecane were obtained.The 9-methylnonadecane was synthesized by the dimerization of 1-deceneusing tri-n-octyl aluminum followed by hydrogenation. This procedure isknow to give 9-methylnonadecane as the predominant C₂₀ product. A sampleof 2-methoxyethanol generated hydrogenated decene dimer preparedaccording to Example 10 was spiked with eicosane and 9-methylnonadecaneand analyzed by gas chromatography. No 9-methylnonadecane isomer wasdetected (less than 0.5 weight percent) in the unspiked sample. Theretention time of the 9-methylnonadecane was the same as the relativelylinear isomer in the 1-butanol/1-propanol generated material.Subsequently, GC/MS analysis confirmed that this isomer was9-methylnonadecane. No eicosane was observed in either product.

Samples of the 2-methylnonadecane generated dimer were then spiked withvarying amount of 9-methylnonadecane and the KV₋₅₄° C. values determinedwith the results shown below:

                  TABLE 4                                                         ______________________________________                                              % Isomer  KV.sub.-54° C.                                                                   KV.sub.-54° C.                               Entry Added     (20 min)  Final   Comments                                    ______________________________________                                        A     0%        1030 cSt  1030 cSt                                                                              Clear, no vis.                                                                change                                      B     1%        1070 cSt  1060 cSt                                                                              Sl. cloudy, 1.5                                                               hour                                        C     3%        2110 cSt  1160 cSt                                                                              Cloudy - 15                                                                   minutes                                     D     5%        1790 cSt  1200 cSt                                                                              Cloudy - 10                                                                   minutes                                     Compar-                                                                             0%        1470 cSt.sup.1                                                                          1220 cSt.sup.2                                                                        Cloudy                                      ison                                                                          ______________________________________                                         .sup.1 at 30 minutes                                                          .sup.2 at 1 hour                                                         

Entries C and D behaved similarly to decene dimer PAO samples derivedfrom 1-butanol/1-propanol co-catalyzed reactions (see "Comparison" inTable 4 which is a hydrogenated dimer derived from a BF₃ /1-propanolcatalyzed reaction), i.e. the KV₋₅₄° C. values were initially high andgradually decreased with time while the mixture became cloudy. The cloudpoint of a commercially available 2.0 cSt PAO fluid, which consisted ofvery pure decene dimer, was -57° C. compared to a cloud point of <-70°C. for a 2-methoxyethanol generated dimer of the invention. Theseresults demonstrate that the dimer products of the invention havesignificantly improved physical properties caused by a difference incomposition from prior I-decene dimer compositions.

Example 11

1-Octene (750.0 grams, 6.70 moles) and 2-methoxyethanol (5.09 grams,67.0 mmoles) were charged into the reactor which was then assembled andpurged with N₂ with gentle agitation for 30 minutes. During this timethe vessel was heated to 45° C. with the circulating system. Thestirring rate was increased (rpm not measured) and BF₃ was introducedinto the reactor via a sparge tube located below the surface of theliquid. After a brief (5-10 seconds) purge, the system was pressurizedto 10 psig with BF₃. An exotherm occurred which reached a maximumtemperature or 64° C. at ˜ 15 minutes.

The reaction was stopped by venting the BF₃ through a 10% NaOH scrubberand then quenching with 5% aqueous NaOH (100 mL). The reaction mixturewas separated from the quenching medium, washed several times withwater, allowed to settle, and filtered through filter paper.

The product contained 5% C₈, 64% C₁₆, 25% C₂₄, and 6% C₃₂ (normalizedgas chromatography area percent).

The crude oligomerization product (1200 g) was hydrogenated in a 2-literautoclave using a Ni/Kieselguhr catalyst (48 g) at 200° C. and 500 psigH₂ for 2 hours. After cooling, the product was filtered throughfilter-aid to give the crude hydrogenated product. The distillation wascarried out at 1.5 mm Hg and the fraction boiling at 107°-120° C. wascollected to give 535 g (1071 g feed) of pure hydrogenated octene dimer.The physical properties were as follows:

    ______________________________________                                               KV.sub.100° C.                                                                       1.09 cSt                                                        KV.sub.40° C.                                                                        2.69 cSt                                                        KV.sub.-40° C.                                                                       71.0 cSt                                                        Pour point    <-65° C.                                                 Flash point   122° C.                                           ______________________________________                                    

The target specifications for an IEC 296 - Class III and III_(A)transformer fluid are:

    ______________________________________                                        KV.sub.40° C.                                                                              3.5 cSt max                                               KV.sub.-40° C.                                                                             150 cSt max                                               Pour point          -60° C. max                                        Flash point         95° C. min                                         ______________________________________                                    

In such use the fluid is contained in an electrical apparatus, i.e. apower transformer. The fluid surrounds an electrical component in theapparatus and acts as an electrical insulating and heat removal medium.

The physical properties of the octene dimer exceeded the transformerfluid specifications and demonstrated excellent low temperatureperformance.

The dimer oils of the invention can be used neat in various heattransfer, insulating and lubricant applications, and when used ininsulating, functional fluid and/or lubricating oil applications suchas, for example, electro erosion, high speed aluminum cold rollingtransformer and switchgear oil, shock absorber, brake, hydraulic textilecovering and spindle fluids, drilling muds and the like, theirproperties can be enhanced by the use of conventional oil additives intotal amounts of up to about 25 weight percent and preferably from about0.1 to 20 weight percent. Such additives include, for example,dispersants, anti-oxidants, anti-wear agents, anti-foam, corrosioninhibitors, detergents, seal swell agents, etc. These types of additivesare well known in the art. Some examples of such additives are zincdialkyl-dithiophosphates, calcium aryl sulfonates, overbased calciumaryl sulfonates, barium phenates, barium oxide neutralized reactionproducts of phosphorus pentasulfide and terpenes or high molecularweight olefins, hindered alkyl phenols, methylene-bis-dialkyl phenols,dibutyl tin sulfide, dibutyl hydrogen phosphonate, tri-cresyl-phosphate,high molecular weight alkyl succinimides of ethylene-polyamines such astetraethylene-polyamine, sulfur-bridged alkyl phenols, sulfurized fattyacid esters and amides, silicones, dialkylesters, and the like. Mixturesof the C₈ and C₁₀ dimer oils in any proportions can be used. The dimercompositions can contain minor amounts of higher oligomers (trimer,tetramer, etc.) but preferably contain at least 60 weight percent andmore preferably at least 75 weight percent of dimers. The dimer oils canbe used as additive oils or as base oils and in blends with mineral oilsand with other synthetic oils such as, for example, synthetic esters.

What is claimed is:
 1. An electrical power transformer, said transformercomprising an electrical component, a synthetic oil surrounding theelectrical component and means for containing said synthetic oil,wherein said synthetic oil is selected from the group consisting of1-octene dimer, 1-decene dimer, co-dimer of 1-octene and 1-decene, andmixtures thereof wherein (a) said 1-octene dimer further consists of amixture of C₁₆ H₃₂ isomers, which mixture includes 7-methylpentadeceneisomers, provided that said mixture contains less than about 2.5 weightpercent of said 7-methylpentadecene isomer based on the weight of saidmixture, (b) said 1-decene dimer further consists of a mixture of C₂₀H₄₀ isomers, which mixture includes 9-methylnonadecene isomers, providedthat said mixture contains less than about 2.5 weight percent of said9-methylnonadecene isomers based on the weight of said mixture, and (c)said co-dimer further consists of a mixture of C₁₈ H₃₆ isomers, whichmixture includes C₁₈ H₃₆ isomers selected from the group consisting of7-methylpentadecene, 9-methylheptadecene isomers, and mixtures thereof,provided that said mixture contains less than about 2.5 weight percentof said 7-methylpentadecene and 9-methylheptadecene isomers based on theweight of said mixture.
 2. The power transformer of claim 1 wherein saidfluid comprises a dimer of 1-octene.
 3. The power transfer of claim 2wherein said fluid contains up to about 25 weight percent of one or moreoil additives.
 4. The power transfer of claim 3 wherein said fluidcontains up to about 0.1 to 20 weight percent of one or more oiladditives.
 5. The power transformer of claim 3 wherein said fluidcomprises a hydrogenated dimer of 1-octene which contains less thanabout 0.5 weight percent of 7-methylpentadecane.
 6. The powertransformer of claim 5 herein said fluid contains an antioxidant.
 7. Thepower transformer of claim 1 wherein said synthetic oil is hydrogenatedso as to provide C₁₆ H₃₄ isomers containing less than about 2.5 weightpercent of 7-methylpentadecane, C₂₀ H₄₂ isomers containing less thanabout 2.5 weight percent of 9-methylnonadecane and C₁₈ H₃₈ isomerscontaining less than about 2.5 weight percent of 7-methylheptadecaneand/or 9-methylheptadecane.